Recovery of metal by use of lead



United States Patent 3,090,686 RECOVERY OF METAL BY USE OF LEAD JohnSimon Nachtman, 2801 Quebec St. NW., Washington, D.C., and Henry GordonPoole, 1000 16th St, Golden, C010. No Drawing. Filed Feb. 19, 1958, Ser.No. 716,033 15 Claims. (Cl. 75-84) This invention relates to methods ofbeneficiating metallic compounds and recovery of metals therefrom aswell as the resulting products, and includes the production of noveltypes of metals having unique properties and methods for producing suchproducts. This application is a continuation-in-part of applicationSerial No. 429,674, filed May 13, 1954, now Patent No. 2,834,671, and ofapplication Serial No. 642,377 filed February 26, 1957, now US. PatentNo. 3,020,151.

The present commercial process for producing molybdenum by the hydrogenreduction of sublimed and recrystallized molybdenum trioxide makes itdiificult to control oxygen without additions of carbon or aluminumduring the arc-melting operation, resulting in detrimental effects ofoxygen nitrogen and carbon upon the physical properties of for example,molybdenum.

One rather obvious approach would be the direct reduction ofmoly-bdenite (MoS l0] metal in a controlled atmosphere. This might beaccomplished by at least four direct methods.

I. Thermal decomposition II. Hydrogen reduction III. Carbon reductionIV. Silicon reduction Thermodynamically silicon is a most desirablereduction agent since it forms a volatile sulfide at say a temperatureof 1227 C. (1500 K.) However, silcon reacts with molybdenum to form arefractory silicide. Carbon also forms a refractory carbide withmolybdenum, and this method also is found wanting. Further an examination of the equilibria for either thermal decomposition or hydrogenreduction indicates a slow reaction rate at 1500 K. particularly withthe former method.

For this type of metallurgical process substantially a complete reactionis needed, circa 100% reduction.

Accordingly prior art methods of producing certain metals from theirores or other compounds, such as molybdenum from molybdenite, involveneedless repetitive processing, and also result in the production ofcontaminated metal.

Among the objects of the present invention is the production of metalsby thermo-chemical treatment of their compounds utilizing reducingagents which result in metals free from contamination with impuritiescommonly pres- 'ent in such metals produced by prior art processes.

Further objects include the production of such metals free from oxygen,chlorine or other halides, sulfur, hydrogen, itrogen, carbon, silicon,and alkali metals.

Further objects include methods of decontamination of metals produced byother processes. I

Further objects include metals resulting from these processes whichmetals have unique compositions and exceptionally high standards ofpurity.

Still further objects and advantages of this invention will appear fromthe more detailed description set forth below, it being understood thatsuch more detailed de- 'scription is given by Way of illustration andexplanation only, and not by Way of limitation since various changestherein may be made by those skilled in the art without departing fromthe scope and spirit of the present invention.

In accordance with the present invention, metals are 3,090,686 PatentedMay 21, 1963 produced by thermochemically treating a sulfide of themetal desired, particularly metals having an atomic number of 27, 28 and42 with lead, the treatment being carried out in a non-oxidizingatmosphere, desirably in the presence of hydrogen, helium or argon, ormixtures thereof at a temperature generally above about 1100 C.sulficient to produce a beneficiated metal.

The process permits the production of molybdenum metal shapes by onestage reduction, compaction, pressure welding and sintering, withoutatmospheric contamination.

The process will be illustrated by the production of high puritymolybdenum and reduced cost free from undesir- .able contaminants and bymethods utilizing lead which thus make it possible to avoid needlessrepetitive processing heretofor required in prior art processes. It hasthus been found that, sulfides of molybdenum may be subjected to directreduction by lead in a non-oxidizing atmosphere, as for example in thepresence of a nonoxidizing gas e.g. hydrogen, helium or argon, ormixtures thereof at temperatures above about 1100 C. Lead, which is ahigh boiling point metal, forms a volatile sulfide and thus makes itfeasible for the stated purposes. Since plumbous sulfide at the order oftemperatures stated, has a vapor pressure that greatly exceeds the vaporpressure of molybdenum sulfide ores, its thermal decomposition products,and molybdenum, vacuum systems may be utilized to accelerate thedesulfurization reaction, and rapidly to purify the molybdenum residue,including direct reduction by lead in the presence of for example hydrogen.

In the reduction of molybdenite for example by lead in the absence ofhydrogen, the probable major reactions are Other reactions, probably ofminor character are:

In the presence of hydrogen, the latter enters the reactions fordesulfurizing molybdenum in two ways. One is aiding the decomposition ofmolybdenite to the sesquisulfide and the other is in decomposing thelead sulfide. These uses can best be summarized in the following seriesof reactions.

But actually the use of hydrogen alone is unsatisfactory because ofequilibria factors. A comparison with lead, shows that in a 12 hourperiod with H of S is removed while a 2 hour period with lead removes:of S Further excessive quantities of hydrogen sulfide are avoided.

The fact that hydrogen reduces the plumbous sulfide during the regularrun subsequent to the desuhiurizing of molybdenum, despite lessfavorable equilibrium data, is kinetically sound since this latterreaction is a gas-gas reaction to produce a gas and a liquid rather thana gassolid to produce gas-solid.

In an actual run at 1250 C. with lead reacted with molybdenite, M08under atmospheric pressure, using stoichiometric amounts of lead, namely30 parts by weight of M05 and 77.6 parts of lead, there were obtained 20parts of molybdenum plus M0 8 90 parts of lead sulfide, PbS, and 8 partsof lead, the resulting pellet having an unreacted core of M0 8 By using20% excess of lead over the stoichiometric amount, namely, 30' parts ofMOS 3 with 93 parts of lead, there was obtained 18 parts of molybdenum,90 parts of PbS, and 15.5 parts of lead, and the resulting pellet showedno unreacted core.

After completion of the reduction of molybdenite to metal, a vacuumsystem at the reaction temperatures permits the volatilization andremoval of any excess metallic lead, if desired, leaving the metallicmolybdenum free of both sulfur and lead.

During reaction in an atmosphere of hydrogen, lead sulfide formed, isreduced in the presence of dry hydrogen to return lead to the reaction.Also lead sulfide which is carried over may be reduced by knownprocedures and the recovered lead returned to the system. Accordinglythe lead process can be carried out in hydrogen with the followingadvantages:

(1) The metallic lead is not consumed since it is readily regeneratedwith hydrogen.

' (2) The carbon content is controlled by hydrogen without the use ofoxide additions other than low partial pressures of water for fixedcarbon.

(3) The cost for vacuum equipment can be eliminated for molybdenumpowder production. This also simplifies retort design.

(4) The circulating hydrogen can be desuliurized by cold traps or othermethods and recirculated.

(5) The reaction rates and temperature requirements are maintained atreadily attainable levels.

The reactions may be carried out over a wide range of temperatures andperiods of time. The temperature employed should at least be about 1100"C. and may be as high as 1450 C. or even higher, the temperature beingpressure dependent since it is desired to retain lead in the liquidphase; but from 1200 to 1300 is preferred. The time may be from about 1to 4 hours, but two hours is a preferable time period. Pressures mayvary. The basic lead reduction is not materially affected by theatmosphere. Helium, hydrogen and argon are desirably utilized atatmospheric pressures. The time may vary with temperature and rate offlow of the non-oxidizing gas present. In hydrogen-lead reduction 3.0 isa desirable lead to molybdenite ratio whereas the stoichiometric ratiois 2.59. The rate of gaseous flow may vary. For example, hydrogen may beused for an 8 hour run at a rate of 1 cu. ft./hr.; for 4 hours at 2 cu.ft./hr.; or 4 cu. ft./ hr. for 2 hours.

The following considerations apply to the control of purity of themolybdenite concentrate. Some of the highest grade products on themarket, advertised at 99+% molybdenite actually contained 1.16+% carbonresulting from cracking of petroleum oils during their distillation fromraw concentrate. The processing of raw materials has become a veryimportant phase of this work since some of the commercially availablematerials seem to have been inadvertently contaminated with carbon. Oneconcentrate obtained by prior art methods appears to be of twoqualities.

(1) Grade I, 7.5% oil, .34 insolubles, .12% Fe., .01% cu. Grade(distilled) II, 1.06% C., 37% SiO +Al O .13% Fe, .01% Cu Grade (leached)III, 1.16% 0., .01% sio +A1 o,,

.16% Fe, .01% Cu (2) Regular grade-5.0% oil, 5.5% insolubles, 1% FeAnother source shows concentrates with three nominal grades and littleor no hydrocarbons.

(1) High grade:

85% MoS 0.15% Cu 85% M08 0.50% Cu 80% M08 1.25% Cu A sample of highgrade No. 1 shipped 7/7/53 analyzed as follows: 92% M08 5.00%insolubles, 0.120% Cu.

The procedure desirably used for preparing molybdenite for reductionprocesses desirably uses the following procedures:

(1) Solvent extraction or distillation of oils in H (2) Leaching withhydrofluoric+hydrochloric acids to remove oxides and allied impurities.

(3) Washing and drying.

While the oils may largely be removed by solvent leaching, as by organicsolvent such as acetone, distillation in H is more desirable.Molybdenite particle size is not critical. 2Sizes available incommercial products average for example 5-7 microns, 13-17 microns, etc.No diflierences have been experienced. Lead has been used for example at200 mesh, 30 mesh, and 20 mesh; also as a molten bath. No differencehave been detected but for operations on a laboratory scale, minus 20mesh is preferred.

As illustrative for beneficiated molybdenite products which areobtainable by the preferred process to control purity of the molybdeniteconcentrate, the following is given, in tabulated form; the feed beingthe initial molybdenite material, the retort product being that afterthe heat treatment of the initial material in an atmosphere of hydrogento give a roasted concentrate, and the final leach product being themolybdenite material ready for H -Pb reduction to produce molybdenummetal.

MOS: H20 011 SiO2+Al20a Fe Feed, percent 70-80 10-15 5-6 4-6 0. 2-1. 0Retort product, percent 89-94 0 0 5-7 0. 3-1. 2 Final leach product,

percent 99. 5 0 0 0. 05-0. 1 0. 05-0. 07

The product is substantially free of carbon, iron and associatedimpurities. The small amounts of SiO+Al O may be beneficial.

THE ADVANTAGES CHEMICAL ANALYSES OF PRODUCTS Sample No. Percent 0Percent S Percent Percent Fe acid insol.

This final leach product may be compared with prior art commercialproducts prior to the present invention and which show:

PRESENT COMMERCIAL PRODUCTS 98.5% M08 1.16% C, 0.05% Swe l-A1 0 .16% FeWhile small quantities of the alumina and iron remain, some of thesilicon is removed as silicon monoxide, the remaining quantity beingsilica. Iron can also be. controlled by special treatment. Most of thecopper and tin report in distilled lead sulfides.

It would appear that most of the market available concentrates may betreated for producing metal without using the special high grade.

The wet HF leaching is satisfactory in plastic containers. There is noneed for heating the mixture, prolonged washing with acid helpsv removeiron.

The preparation of materials for reduction in the furnace may usevarious techniques. Loosely mixed granular lead and molybdenite willreact, however, it is preferred and recommended that the materials bebriquetted. This briquetting may for example be carried out as follows:

(a) Mixture of M03 and granular lead is briquetted. For example, insmall scale operations both /2 inch and 1 inch round dies have beenemployed with pressures of 8000-25300 pounds per square inch.

(b) The M08 may be briquetted and partially or wholly immersed in liquidlead. Under conditions so far employed the M08 and lead should be incontact. The molybdenite briquette is not normally wetted by molten leadat atmospheric pressures and low temperatures.

Consideration should be given to vapor pressures. Lead boils at 1750 C.and at the boiling point of lead sulfide (1250-80 C.) has a vaporpressure of 20 to 30 mm. Hg. The lead may boil off at the reactiontemperature, so that at least 20% excess lead is desirable. Furthermorethe molten lead does not wet the decomposing molybdenite as did the tin,therefore it is desirable to enclose the reacting pellet partially sothat the lead does not run away. This may be done by placing the pelletof 20 mesh granulated lead plus molybdenite compressed at 10,000 to20,000 lbs. per sq. in. in a molybdenum boat.

The molybdenum metal briquettes when produced are sponge like andcapable of re-compression. Thegrain size of the reduced molybdenite isvery small and approximate 2-3 microns. However it will vatry withsource of raw materials.

Various additives for any of the pure metals obtained under this processor otherwise may be included in the methods set forth above for specialeffiects or results. These additives may be conveniently considered intwo general classes:

I. Inert during sulfide reduction stage:

(a) Elemental W, Co, Ni, Nb, Ir.

II. After reduction to pure molybdenum powder:

(a) Ni, Cr, Zr, Ti, Hf, Co, Ta, Th, W, Al, C-b,

Be, Ir.

(b) Oxides and oxygen bearing compounds of the metals enumerated inII(a) such as zirconates, titanates, alurninates, aluminides, etc. andalso the rare earths.

The above additions as set forth in I and Il may be added to the Mopowder and mixed, then sintered or briquetted. The briquetted materialsmay be extruded or rolled. The sintered materials may be melted,hotpressed, extruded, cold-pressed or rolled. The sintering andmechanical operations should desirably be carried out undernon-oxidizing conditions.

Since in the processes of the present invention, it is desired to makeductile metal, i.e. molybdenum, substantially free from oxygen,hydrogen, and nitrogen, the addition of oxides or oxygen containingcompounds is only for the purpose of obtaining certain desirablephysical properties and also to a controlled extent the oxidation ofmolybdenum at elevated temperatures. Thus certain oxides and oxygenbearing compounds are added to control grain size or to clean up grainborders.

The metal and alloy additions are also for the purpose of obtainingcertain desirable physical properties in the metals. The amounts of theadditions may vary with the additives and the metal to which added. Ingeneral, oxides or oxygen bearing compounds may be added in amounts byweight of about 0.1 to on the weight of the metal to which they areadded. The amounts of metal or alloy additives may vary much moreWidely. Nor are the various additives equivalents in their actionssince, for example, oxides and oxygen bearing; compounds have differenteifects upon the pure metal to which they are added, depending on theaddition made.

While the invention has been particularly described with respect toreduction of molybdenum, cobalt, or nickel containing sulfide ores byuse of lead, in many instances it is desirable to use an alloy of leadwith tin for reduction, desirably in eutectic ratios. Not only mayeconomies be secured in this way, but by the use of such alloys, theamount of excess lead desirably used may be reduced by keeping the leadin place. And when an atmosphere of dry hydrogen is employed duringreduction, a leadtin alloy in the correct proportions gives much bettercontrol of the amount of metal required, for reduction of the sulfides.

The following example will illustrate the invention, parts being byweight unless otherwise indicated.

Example Molybdenite-lead pellets were made by mixing 20 mesh granulatedlead with powdered molybdenite in the ratio of 93 parts to 30 parts andcompressed at 20,000 lbs/sq. in. into cylindrical pellets of /idiameter. The pellets were placed in a molybdenum boat and subjected ina furnace to a temperature of about 0 C. for about four hours. A tubefurnace was used large enough to permit gas passage. 18 parts ofmolybdenum metal sponge were recovered after completion of the reaction.The reaction is facilitated by sweeping PbS away from the pellet by flowof a non-oxidizing gas such as argon at a rate of approximately 2 cu.ft/min. using a 1 /2 (inside diameter) reaction tube in a globarfurnace.

Cobalt or nickel containing sulfides may be reduced in an analogousmanner using amounts of such sulfides in ratios equivalent to theamounts of molybdenum sulfide ore. Both cobalt and nickel sulfides formlow melting eutectics with metal at 600900 F. If the reactions arestarted at low temperatures and are increased to 1200-1300 C., nickeland cobalt sulfides may be retained as solid phase. If the reactionsstart at 1200 to 1300 0, natural cobalt and nickel sulfides may beliquids until the composition is less than 10% sulfur for nickel andless than 20% sulfur for cobalt. In some cases, therefore, depending onthe nature of the sulfides and reacting conditions the sulfides may beliquid during reduction and may be solids in other cases and thisapplies to molybdenite as well as nickel and cobalt sulfides.

The following examples further illustrate the invention.

By increasing-the hydrogen flow, over 50% of Sn and Pb will be reducedfrom sulfides, thus increasing H 5 production.

Briquette The'l'eadreduction of M08 should be carried out in a refluxtype system. Hence the lead which boils 011? will return, thuseliminating need for 20% excess in briquette. Furthermore, carrying outthis reaction in H will permit even smaller proportions thanstoichiometric lead to be used in the briquette. It is relatively simpleto distil off excess lead from finished molybdenum metal sponge.

These examples may be carried out under the general operation as in thefirst example set forth above with such changes as the individualexamples indicate. In general where nickel or cobalt containing sulfidesare used, equivalent amounts may be substituted for the molybdenumsulfide.

The following data is of interest in connection with the operations setforth herein.

Melting points, C.

Ores, particularly sulfide ores, useful for treatment in connection withthis invention include: for cobalt, cobaltite CoAs S linnaeite (Ni, Co)S for molybdenum, molybdenite MoS for nickel, pentlandite (Fe, Ni)S,millerite NiS, linnaeite (Ni, Co) S etc.

Since different metals have difierent effects upon the molybdenum, inmany cases it is desirable to reduce molybdenite with zinc, cadmium,antimony or bismuth, and mixtures thereof, with or without lead and/ ortin. The reduction will desirably take place at the temperature between1100" C. and 1450 C. and the amounts may desirably be in stoichiometricproportions. The reduction may-be carried out under non-oxidizingconditions, such as in the presence of hydrogen, helium or argon, and ifdesired under vacuum, a hydrogen atmosphere being preferred.

Having thus set forth our invention, we claim:

1.-In the method of producing a metal selected from the group consistingof cobalt, nickel, molybdenum and alloys thereof from the correspondingmetal sulfides, heating the metal sulfide with lead in a non-oxidizingatmosphere at a temperature of from about 1100 C. to below about 1450 C.whereby a reduction reaction takes place between the metal sulfide andlead to produce the purified metal.

2. The method of claim 1 in which the metal sulfide is molybdenumsulfide. 3. The method of claim 1 in which the metal sulfide is nickelsulfide. v4. The method of claim 1 in which the metal sulfide is cobaltsulfide.

5. The method of claim -1 in which the reduction is carried out in thepresence of hydrogen.

6. The method of claim 5 in which the sulfide is molybdenum sulfide.

'7. The method of claim 5 in which the sulfide is nickel Jsulfide. V V VV V 8. The method of claim 5 in which the sulfide is a'co baltcontaining sulfide.

9. The method of claim 1 in which the reduction is carried out in thepresence of helium.

10. The method of claim 9' in which the sulfide is molybdenum sulfide.

11. The method of claim 9 in which the sulfide is nickel sulfide.

12. The method of claim 9 in which the sulfide is a cobalt containingsulfide.

13. The method of claim 1 in which the reduction is carried out in thepresence of argon.

14. The method of claim 13 in which the sulfide is molybdenum sulfide.

15. The method of claim 13 in which the sulfide is nickel sulfide.

16. The method of claim 13 in which the sulfide is a cobalt containingsulfide.

17. In the method of producing a metal selected from the groupconsisting of cobalt, nickel, molybdenum and alloys thereof from thecorresponding metal sulfide comprising heating the metal sulfide withlead in a non-oxidizing atmosphere at a temperature of from about 1200C. to about 1300 C. to reduce said metal sulfide with lead to producethe corresponding purified metal.

18. The method of claim 17 in which an adjuvant metal selected from thegroup consisting of W, Co, .Cb, Ir and Ni is added in the reduction zonein a form which gives a resultant alloy upon reduction.

19. In the method of producing molybdenum from its ores heating solidphase molybdenite while in a solid phase with a metal selected from thegroup consisting of zinc, cadmium, antimony and bismuth lead and themixtures thereof at a temperature of from 1100 C. to below about 1450 C.

References Cited in the file of this patent UNITED STATES PATENTS855,157 Becket May 28, 1907 1,022,595 Rossi Apr. 9, 1912 1,096,464Schwarzkopf May 12, 1914 1,175,693 Bosch et a1. Mar. 14, 1916 1,221,873Ladofi Apr. 10, 1917 1,373,038 Weber Mar. 29, 1921 2,665,474 Beidler eta1. Jan. 12, 1954 2,678,268 Ham May 11, 1954 2,678,269 I-Iam May 11,1954 2,834,671 Nachtmann May 13, 1958 OTHER REFERENCES Metal Progress,July 1961, pp. 86-88.

1. IN THE METHOD OF PRODUCING A METAL SELECTED FROM THE GROUP CONSISTINGOF COBALT,NICKEL,MOLYBDENUM AND ALLOYS THEREOF FROM THE CORRESPONDINGMETAL SULFIDES, HEATING THE METAL SULFIDE WITH LEAD IN A NON-OXIDIZINGATMOSPHERE AT A TEMPERATURE OF FROM ABOUT 1100*C, TO BELOW ABOUT1450*C.WHEREBY A REDUCTION REACTION TAKES PLACE BETWEEN THE METALSULFIDE AND LEAD TO PRODUCE THE PURIFIED METAL.